Apparatus for internally coating pipes

ABSTRACT

An apparatus for coating the internal surfaces of pipes comprises two pigs which engage against the internal pipe surfaces and are movable through the pipe, and which define an intermediate zone therebetween for receiving the coating material. A spraying device capable of spraying material in the radial direction is connected to the intermediate zone via a material feed line. Upon being drawn through the pipe, the coating material is fed to the spraying device which atomizes the material and conveys it to the internal surfaces of the pipe.

TECHNICAL FIELD

The invention relates to an apparatus for the internal coating of pipeshaving a first and second pig which engage the internal pipe surface andare movable through the pipe, having an intermediate zone between thetwo pigs for receiving coating material, whereby during the movement thepigs are pressurized and the coating material is forced out of theintermediate zone onto the internal surfaces of the pipe.

BACKGROUND OF THE INVENTION

In the chemical field, in particular in natural gas and oiltransportation, water containing aggressive components (sulfur, salt)occurs in considerable quantities. This water is transported throughwelded steel pipes at times under very high pressures (up to 200 bar).If these are not isolated from the inside, they are destroyed bycorrosion in a short time, which adversely affects the operation andconsiderably endangers the environment.

To reduce corrosion it has been suggested to install plastic tubeswithin the steel pipes. This, however, leads to an undesirable reductionof the pipe cross section.

For the prevention of this effect, it is known to coat the interior ofpipes with material which is resistant to the accumulated aggressivemedia. This coating is carried out in pipes of large diameters by meansof mobile vehicles which spray coating material.

This is not possible for pipes of small diameters. Instead, they may becoated, for example, by a package consisting of two pigs between whichthe in general fluid coating material is located, which is drawn backand forth through the pipe. Such a procedure has the disadvantage thatthe weak points which occur in the region of uneven parts of theinternal pipe surface, particularly at the weld seams, where the coatingmaterial is stripped off by the second pig and thus form attack pointsfor the aggressive media.

Another process for coating is airless paint spraying (the so-calledairless-process). In this, the coating material from a tank locatedoutside the pipe is pumped to a nozzle in the pipe by means of a highpressure pump and a high pressure tube. The high pressure in the tubecauses the material to be sprayed and coat the internal surface of thepipe. The disadvantage of such a system is that, as a result of theconsiderable pressure loss caused by friction in the high pressure pipeonly limited pipe lengths may be coated.

Even in oil and natural gas transportation, piplines are provided forthe transport of required substances which may in parts extendunderground for long stretches and so the new coatings of the inner tubesurfaces required at regular yearly or half-yearly intervals causes aconsiderable expenditure. In order to effect the interval coating by oneof the known apparatuses, stretches of about 300 m are dug up and thetube cut apart.

SUMMARY OF THE INVENTION

An object of the invention is therefore to provide an apparatus whichenables very long thin pipes to be uniformly and reliably coated on theinside without permitting the coating to become too thin or completelybroken at irregularities of the internal pipe surface.

This object is achieved by providing a spraying device which is movablethrough the pipe and which is connected to the intermediate zone betweenthe pigs by means of a material feed line and the coating material fromthe intermediate zone is used for spraying.

By the use of such an apparatus, the coating material is carried alongin the immediate vicinity of the spraying device so that practically nopressure loss takes place on the delivery to the spraying device; at thesame time, the atomizing spraying device creates a non-contact, eveninner coating of the pipe even at the weld seams and other uneven partsof the inner surface of the pipe.

Moreover, the pigs, which engage elastically with the pipe innersurface, spread the coating material located in the intermediate zone onthe pipe inner surface as a thin base film so that pores andindentations that are difficult for the spraying device to access arealready coated with the coating material when the spraying devicereaches such regions.

Regions, particularly at the weld seams, from which the second pigremoves the coating right down to a base film, are further covered withnew coating material by the spraying device which preferably actsradially.

Using the apparatus of the invention pipes of lengths several timesthose of which may be sprayed with conventional equipment, can be spraycoated. The number of expensive excavation points, in the case of pipesextending underground, can thus clearly be reduced. By reason of theeven internal coating, it is also possible, if necessary, to increasethe time intervals between two successive coating operations.

A particular advantage is obtained when the spraying device has aspinning wheel or a rotating nozzle which is caused to rotate bycompressed air from a compressed air reservoir. Alternatively, anelectric motor can be used as the drive or a non-rotating spray nozzlemay be provided.

In order to atomize the coating material, the material may bepressurized either by compressed air from the compressed air reservoiror by feed pressure from an electric conveyor pump which, by means of aconveyor element which projects into the intermediate zone, forcescoating material through the material feed line to the spray nozzle.

Preferably, pull cords are attached to the second pig and extend throughthe intermediate zone and the first pig and are coupled to a cord winchlocated outside the pipe. By pulling the pull cords, the coatingmaterial in the intermediate zone is pressurized and fed to the sprayingdevice through the material feed tube by the consequent increasedpressure. A conveyor pump for the transportation of the coating materialto the nozzle of the spraying device is not necessary in this embodimentof the invention.

It is advantageous, if the compressed air tube in the intermediate zoneand between the compressed air reservoir and the first pig isintrinsically elastic and spirally wound. It can then adapt itself tothe reducing quantity or respectively the reducing distance of the twopigs.

In order to allow for rotational movement of the pigs, the attachmentsof the compressed air feed tube may be via rotatable couplings.

Further preferred features of the invention are defined in the dependentclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, three working embodients of the invention aredescribed in detail with reference to the accompanying drawing. Itshows:

FIG. 1 a longitudinal cross-section of a pipe containing an embodimentof the apparatus of the invention;

FIG. 2 a longitudinal cross-section of a pipe containing a secondembodiment of the apparatus of the invention; and

FIG. 3 a longitudinal cross-section of a pipe containing a thirdembodiment of the equipment.

DETAILED DESCRIPTION OF THE INVENTION

A pipe 10 is to be provided on its inner surface with an internal layerof coating material 16.

The apparatus used for the internal coating according to FIG. 1 has acompressed air reservoir 20 with a pressure of, for example, 200 barwhich is secured by slide collars 21. It is provided with a highpressure shutoff valve 22 which a pressure reducer 23 is connected. Theoutlet of the pressure reducer is located on the axis of the axiallysymmetrical apparatus and consequently also on the axis of the pipe.

An elastic, spirally-wound pressure tube 30a is attached to the pressurereducer 23. The spiral winding is concentric with the axis of theapparatus and the pipe. The tube 30a may also rotate freely since it isattached to the pressure reducer via a rotatable coupling 31a.

The end of the pressure tubing 30a opposite to the compressed airreservoir 20 is connected via a rotatable coupling 31b to a solidconduit section 32a in a first pig 40. The pig 40 consists of severalspaced layers which completely occupy the cross sectional area of thepipe and have elastic outer edges which engage against the inner surfaceof the pipe.

The solid conduit section 32a of the pressure tubing 30 runs along theaxis of the first pig 40. On the other side of the pig 40, a furtherspirally-wound section 30b of the pressure tubing 30 is locatedconcentrically to the axis of the apparatus and is attached to theconduit section 32a via a rotatable coupling 31c. This leads to a solidconduit section 32b located in a second pig 41, and is attached theretovia a rotatable coupling 31d. The second pig 41 is constructed in thesame way as the first pig 40 and likewise occupies the entire crosssectional area of the pipe. An intermediate zone 42 is located betweenthe two pigs 40, 41 which is occupied by coating material 16.

Two pull cords 50a, 50b are attached to the second pig 41 by means ofeyelets 51. The pull cords 50a, 50b extend symmetrically parallel butnon-centrally from the second pig 41, through the intermediate zone 42to the first pig 40 through which they extend via sealing bushings butto which they are not attached. The pull cords 50a, 50b then extendfurther to eyelets 53 on the compressed air reservoir 20. From there thepull cords 50a, 50b separately extend from further eyelets 53 to acommon eyelet 54 located on the axis of the apparatus, and from this anaxially-extending pull cord 50c extends to a cord winder (not shown) atthe end of the pipe 10.

The solid conduit 32b of the pressure tubing 30 which extends throughthe second pig 41 is provided with a sbutoff valve 33 on the side of thepig 41 opposite to the intermediate zone 42. From there, the compressedair tubing 30 extends to spray apparatus 70, 71 which is rigidly fixedto the second pig 41 and which comprises a compressed air turbine 70carrying a rotational nozzle 71.

The pig 41 additionally has coating material feed tubes 60 extendingthrough it and the open ends of the tubes communicate with theintermediate zone 42 and with the rotational nozzle 71.

The internal coating of the pipe 10 takes place in the following manner:

After cleaning of the internal surface 11 of the pipe the entireapparatus is pulled through the pipe by means of a cord winch in thedirection opposite to the coating direction (arrow 15). Alternatively,the pull cord 50 may be shot or pulled through the pipe 10. Next, theindividual parts are then combined with each other in a separate,additional pipe piece (not shown) and the intermediate zone between thepigs 40 and 41 filled with coating material 16.

A preferably steplessly acting winch pulls the compressed air reservoir20 and the second pig 41 through the pipe 10 via pull cords 50c, 50a,50b at a predetermined speed. The first pig 40 is not pulled by any ofthe pull cords but it is pushed in the direction of pull by the coatingmaterial 16 which dams up in front of the second pig 41 in theintermediate zone 42. The pressure thereby generated drives the coatingmaterial 16 through the material feed tubes 60 into the rotary nozzle 71of the compressed air turbine 70. The compressed air drives thecompressed air turbine 70 upon corresponding actuation of the shutoffvalves 22, 23 at a rotational speed of, for example, 20,000 rpm. Thehigh rotational speed causes the coating material 16 to be atomized. Astream of atomized coating material 16 is then sprayed from the rotarynozzle 71 onto the internal surface 11 of the pipe.

Upon movement of the apparatus through the pipe 10, the second pig 41spreads further coating material behind it from the intermediate zone 42directly onto the internal surface of the pipe, and the spray coatingfrom the spray equipment then forms on this primer layer.

As coating proceeds, the supply of coating material 16 in theintermediate zone 42 between the two pigs 40, 41 diminishes. The coatingspace 42 thus becomes smaller, and the two pigs 40, 41 draw closer toeach other. The pressure tube 30b in the intermediate zone 42 then has asmaller axial length to traverse; the spiral windings are therebypressed together.

Conversely, the distance between the two rotatable couplings 31a, 31b,and therefore the distance between the pressure reducer 23 of thecompressed air reservoir 20 and the first pig 40 increases, because thedistance between the compressed air reservoir 20 and the second pig 41remains constant. The section 30a of the compressed air tube 30 mustconsequently bridge a longer axial distance, and its spiral windings aretherefore drawn apart.

The rotational couplings 31 in the compressed air tubing 30 are providedto accommodate forces which may arise as a result of rotary motions ofthe pigs 40, 41.

The second embodiment shown in FIG. 2 is largely similar to the firstembodiment. Instead of the compressed air supply, an electric motor 70'is located in the spray device 70', 71. This is provided with currentthrough an electrical lead 57, which is provided as a core in the pullcord 50. The pull cord 50 extends through sealing bushings in the firstpig 40, through the intermediate zone 42, and is attached to the secondpig 41 at the attachment point 56.

Metering valves 61 are provided in the coating material feed tubes 60for better matching of the coating material flow with the coating speed(speed of progression of the apparatus through the tube) and adjustmentof the coating thickness on the internal surface 11. A normallydesirable coating thickness is about 400 μm.

The embodiment shown in FIG. 3 comprises, if necessary, a first pig 40and a second pig 41, between which the intermediate zone 42 is providedand which is filled with the coating material 16. A central eyelet 56 islocated on the second pig 41 on which the pull cord 50 is fastened. Thepull cord extends through the intermediate zone 42, through a central,sealing bushing 52 in the first pig 40 and to an end of the pipe 10. Thepull cord 50 is movable relative to the sealing bushing 52 so that thefirst pig 40 may approach the second pig 41 as the coating material 16is depleted from the intermediate zone 42.

A booster pump 80 is located behind the second pig in the pullingdirection by means of coupling links 85. The pump is driven by anelectric motor 81 and is centrally positioned in pipe 10 by slidingelements 21. A booster element 82 of the booster pump 80 extendsrearwardly from the electric motor 81 through the second pig 41 andfeeds the coating material 16 into the opening of the material feed line60, which in turn extends through the second pig 41, via a meteringvalve 61 for the coating material to the nozzle 71 of the spray device.The spray device 70', 71 is coupled via coupling links 85 behind thebooster pump 80, 81 and is positioned centrally in the tube 10, ifnecessary, by means of sliding elements 21. The nozzle 71, which isrotated by an electric motor 70', then sprays the coating materialuniformly against internal surface of the pipe.

I claim:
 1. Apparatus for internally coating pipes comprising a firstand a second pig which engage the internal surface of the pipe and aremoveable through the pipe to form a primer layer on the internal pipesurface, an intermediate zone between the two pigs for receiving coatingmaterial, said coating material being pressurized when moving the pigsto drive said coating material from the intermediate zone through amaterial feedline to a spray device structurally attached to the secondpig, said spraying device spraying coating material received from theintermediate zone onto the primer layer formed by the pigs.
 2. Apparatusaccording to claim 1, characterized in that the spraying device (70, 71)is located behind the second pig (41) and that the material feed line(60) extends through the second pig (41).
 3. Apparatus according toclaim 1, characterized in that a pull cord (50) is fixed to the secondpig (41) and sealingly extends through the first pig (40) via sealingbushings (52) and is connected to a cord winch at one end of the pipe(10) for movement of the pigs (40, 41).
 4. Apparatus according to claim1, characterized in that the spraying device (70, 71) is connected to acompressed air reservoir (20) via a compressed air tube (30a,30b) forthe spraying of coating material (16).
 5. Apparatus according to claim4, characterized in that the spraying device (70, 71) comprises a rotarynozzle which is rotatably driven by means of compressed air from thecompressed air reservoir (20) or by means of an electric motor (70'). 6.Apparatus according to claim 4, characterized in that the compressed airreservoir is located in front of the first pig (40) or between thesecond pig (41) and the spraying device (70, 71) and is slidable in thepipe on sliding elements (21).
 7. Apparatus according to claim 6,characterized in that the compressed air reservoir (20) is arrangedbefore the first pig, that the compressed air tube (30a,30b) connectingthe compressed air reservoir (20) and the spraying device (70, 71)extends through the first pig (40) and the intermediate zone (42) and isspirally wound in the intermediate zone (42).
 8. Apparatus according toclaim 1, characterized in that an electric booster pump (80, 82) isprovided which enhances the flow of coating material (16) from theintermediate zone (42) through the material feed line (60) to the nozzleof the spraying device (70', 71).
 9. Apparatus according to claim 8,characterized in that the booster pump (80, 82) is located in front ofthe first pig (40) or between the second pig (41) and the sprayingdevice (70', 71) and contains a booster element (82) which projectsthrough one pig (40, 41) into the intermediate zone and forces thecoating material (16) into the material feed line (60) to the nozzle ofthe spraying device (70', 71).
 10. Apparatus according to claim 1,characterized in that a metering valve (61) is arranged in the materialfeed line (60).
 11. Apparatus for internally coating pipes having afirst and a second pig which engage the internal pipe surfaces and aremovable through the pipe, having an intermediate zone between the twopigs for receiving coating material, whereupon during the movement thematerial between the pigs is pressurized and the coating material isforced out of the intermediate zone onto the internal surfaces of thepipe, characterized in that a spraying device which is movable throughthe pipe is located behind the second pig and is connected to theintermediate zone between the pigs via a material feed line extendingthrough the second pig where said spraying device sprays coatingmaterial from the intermediate zone.
 12. Apparatus for internallycoating pipes having a first and a second pig which engage the internalpipe surfaces and are movable through the pipe, having an intermediatezone between the two pigs for receiving coating material, where movementis induced by a pull cord is fixed to the second pig and sealinglyextends through the first pig via sealing bushings and is connected to acord winch at one of the pipe for movement of the pigs; during movement,the material between the pigs is pressurized and the coating material isforced out of the intermediate zone onto the internal surfaces of thepipe, characterized in that a spraying device which is movable throughthe pipe is connected to the intermediate zone between the pigs via amaterial feed line and sprays coating material from the intermediatezone.
 13. Apparatus for internally coating pipes having a first and asecond pig which engage the internal pipe surface and are movablethrough the pipe, having an intermediate zone between the two pigs forreceiving coating material, whereupon during the movement the materialbetween the pigs is pressurized and the coating material is forced outof the intermediate zone onto the internal surfaces of the pipe,characterized in that a spraying device which is movable through thepipe is connected to the intermediate zone between the pigs via amaterial feed line, said spraying device comprising a rotary nozzlewhich is rotatably driven by means of compressed air from the compressedair reservoir.
 14. Apparatus for internally coating pipes having a firstand a second pig which engage the internal pipe surfaces and are movablethrough the pipe, having an intermediate zone between the two pigs forreceiving coating material, whereup during the movement the materialbetween the pigs is pressurized and the coating material is forced outof the intermediate zone onto the internal surfaces of the pipe,characterized in that a spraying device which is movable through thepipe is connected to the intermediate zone between the pigs via amaterial feed line and sprays coating material from the intermediatezone where an electric booster pump is provided which enhances the flowof coating material from the intermediate zone through the material feedline to the nozzle of the spraying device.
 15. Apparatus for internallycoating pipes having a first and a second pig which engage the internalpipe surfaces and are movable through the pipe, having an intermediatezone between the two pigs for receiving coating material, whereuponduring the movement the material between the pigs is pressurized and thecoating material is forced out of the intermediate zone onto theinternal surfaces of the pipe, characterized in that a spraying devicewhich is movable through the pipe is connected to the intermediate zonebetween the pigs via a material feed line, with a metering valvearranged therein, and sprays coating material from the intermediatezone.